There is today an increasing demand from passengers to be able to communicate through mobile phones and other handheld terminals when travelling on trains, and also to be able to get access to the Internet with laptops, PDAs etc. However, train carriages are made of metal, and even the windows are normally covered with a metal film. Accordingly, train carriages are shielded compartments, and direct communication between terminal antennas within the carriages and externally located antennas is difficult to obtain. Further, with the new smartphones, and the way these are used, with e.g. continuously operating applications, many phones are active at all times, meaning that many handovers are required when the train moves. Even though this problem is common for all moving vehicles, it is especially pronounced for vehicles moving at high speed, such as trains.
To this end, train carriages are often provided with an external antenna connected to a repeater unit within the carriage, which in turn is connected to an internal antenna. Hence, the communication between the passengers' terminals and the operator antennas outside the trains occurs through the repeater unit. Similarly, it is known to provide a mobile access router for data communication, also connected both to an external antenna and an internal antenna, in each carriage, in order to provide Internet access on-board the train. Such mobile access router solutions are e.g. commercially available from the applicant of the present application, Icomera AB, of Gothenburg, Sweden, and are also disclosed in EP 1 175 757 by the same applicant. However, the aforementioned solution is often insufficient to obtain an optimal transmission performance, especially for large data volumes. Trains and other moving vehicles often pass through areas with bad radio coverage, and present solutions are often unable to handle the required traffic.
At the same time, broadcast television and radio networks are currently being replaced with digital media services based on the Internet, where video and audio is downloaded to consumers using the Internet Protocol (IP), as they are being consumed. These “streaming” media services offer a vastly wider range of content than traditional television and radio, both live and on demand.
Streaming video of high quality requires consistently high throughput of data. Consistency is needed in part because content providers do not wish to expend bandwidth on data that is not eventually viewed, and therefore offer on-demand video at the rate it is being watched, with a short buffer to handle temporary problems. Live streaming cannot, by definition, be protected by a long buffer, and is correspondingly more sensitive.
To this end, solutions such as adaptive bitrate have been developed. As an example, HTTP Live Streaming (HLS) is a media streaming communications protocol that works by breaking the overall stream into a sequence of small files/segments, commonly called “chunks”, each downloaded via HTTP and containing a brief section of the content. An extended M3U playlist allows the client to select interchangeable chunks from a number of different sub-streams. These contain the same media material, such as a feature film, but encoded at a variety of bitrates, typically with different resolution, audio compression severity etc. By this method, the viewer can compromise between quality and possible “stutter” in delivery. If the viewer does not choose a sub-stream manually, software algorithms will normally choose one that appears to match the performance of the viewer's Internet connection. Some competing protocols, such as Dynamic Adaptive Streaming over HTTP (DASH, now an international standard) use the same mechanism.
Generally more efficient encoding of video and audio have also improved the quality of streaming media over the past 20 years, relative to data throughput. Another form of improvement is the wide distribution of content mirrors, i.e. servers replicating media content, so that each client gets a relatively short path to the nearest source of a given stream.
Viewer expectations rise at a rate similar to that of improvements in quality resulting from these innovations. Expectations remain difficult to meet in bandwidth-constrained situations, such as mobile devices on wireless network links. Wireless links remain inferior in throughput to wired links in concurrent development. The available throughput, and the reliability of that throughput, are especially poor on moving vehicles.
In motion, Rayleigh fading and interference frequently defeat the mechanisms in place to alleviate the smaller range of problems that exist in media streaming to wired devices. This is especially true if multiple, rapidly moving users each have a personal wireless link, such as a 4G (e.g. LTE) modem or personal mobile telephone. This is because the resources available from wireless infrastructure are commonly overtaxed by a large amount of users with high bandwidth requirements, particularly in rural areas, where the infrastructure is generally poor. A metal fuselage or other vehicle exterior with windows tinted by metallic film forms a Faraday shield, another common cause of signal degradation in wireless transmission to personal modems inside vehicles.
The situation is similar when multiple users share a connection from a moving vehicle to the Internet, such as discussed above. This is the case on some public transportation buses and light rail as well as long-distance passenger trains, planes and ferries with hundreds of passengers with an on-board network. On such networks, external connectivity is typically provided by a satellite or wireless wide-area network (WWAN) link, or any small set of such links. In this scenario, the antennas are likely external to the vehicle and therefore outside the Faraday shield of the vehicle's body. However, the congestion that results from multiple users trying to retrieve their own copies of the same media stream can still cause most or all of these users to receive a low-quality sub-stream at an uneven pace.
With or without a shared link, the worst-case scenario is multiple users trying to access a popular live video stream. Examples of such streams would be live news reports and major sporting events, where several hundred passengers on a single vehicle may realistically want to watch the video on private devices. A live stream that cannot be delayed by the individual clients having to buffer content locally will instead become unavailable as a result of competition for bandwidth bringing average throughput near or below the threshold of even the lowest-bitrate sub-stream.
Streaming media the way it is currently done uses far more data per minute of journey per passenger than older uses of the Internet, such as browsing text- and image-based sites like Facebook, or checking and responding to email. WWAN links from a vehicle to the Internet, including 4G links, are typically associated with a significant cost. This is especially true with multiple, concurrent users of each single link, as is the case with Wi-Fi services on board a passenger train. An on-board network that uses data services provided by third parties can therefore represent a significant part of the monthly running costs of a vehicle for some operators. Therefore, even if there is sufficient bandwidth available for the streaming of media at reasonable quality to each user, the amount of data such usage incurs can prove a financial issue for the vehicle operators, who are looking to get the best return on investment for the data that they purchase.
There is therefore a need for an improved method and system for receiving streaming media from an external provider onboard a moving vehicle via wireless communication, which provides better capacity utilization, quality and/or cost-efficiency. Even though the above discussion is focused on trains, similar situations and problems are encountered in many other types of moving vehicles, and in particular moving passenger vehicles, such as buses, ships and airplanes.